## 8.49 [ENDORSED]

$\Delta U=q+w$

Hyein Cha 2I
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### 8.49

Oxygen diflouride is a colorless, very poisonous gas that reacts rapidly with water vapor to produce O2, HF and heat: OF2 +H20 yields O2 +2HF and delta H is =- 318 kJ.

I just don't get why T remains constant when calculating for -PdeltaV = -deltanRT.

Also, why is T 298K and not other temperature? The question does not give any info about T, but solutions manual says that T=298K.

Chem_Mod
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### Re: 8.49  [ENDORSED]

We will usually take chemical reactions as occurring in isothermal environments. This is the basis for standard molar enthalpies of formation and standard reaction enthalpies we have discussed and can be found tabulated in the back of the book. All these values are predicated on the fact that temperature and pressure remain constant.

It will usually be pretty obvious from the problem description when temperature changes occur.

Hyein Cha 2I
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### Re: 8.49

Chem_Mod wrote:We will usually take chemical reactions as occurring in isothermal environments. This is the basis for standard molar enthalpies of formation and standard reaction enthalpies we have discussed and can be found tabulated in the back of the book. All these values are predicated on the fact that temperature and pressure remain constant.

It will usually be pretty obvious from the problem description when temperature changes occur.

So will T always be 298K? If no info about T is given in the problem, do we just assume it's 298K?

mhuang 1E
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### Re: 8.49

From what I read on another post, it's said that if the temperature is not explicitly statedg, we can assume that the reaction is occurring at standard temperature, which is 25C (room temp) or 298K.

Ramya Lakkaraju 1B
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### Re: 8.49

Yes, if no other temperature is given in the problem, it is safe to assume that the reaction occurred at room temperature which is 298 K.